1. Technical Field of the Invention
The present invention relates generally to a needle device for a so-called infusion set with which parenteral liquid is infused into a human body. More particularly, the present invention relates to an improvement of an infusion needle device of the type including a liquid delivering passage and an air introducing passage extending in parallel with each other.
2. Description of the Prior Art
In general, a parenteral liquid infusion set is constructed such that a needle device is provided at one end for allowing a tubular needle to be pierced into the interior of a parenteral liquid container and a vein needle is provided at the other end for allowing a patient's vein to be pierced. In addition, the infusion set includes a drip chamber and a flexible tube extending between the needle device and the vein needle. The conventional needle devices required for the infusion set are classified into two types, i.e., one type including only a liquid delivering passage with an air introducing passage being provided separately and the other type including a liquid delivering passage and an air introducing passage extending in parallel with each other. A few examples of the needle device of the last-mentioned type are disclosed in official gazettes as Japanese Published Utility Model NO. 36400/1976, Japanese Laid-Open Utility Model NO. 30232/1985 and Japanese Laid-Open Utility Model NO. 30233/1985. Specifically, the needle device disclosed in Japanese Published Utility Model NO. 36400/1976 involves a needle tube divided into two passages, one serving as a liquid delivering passage and the other serving as an air introducing passage. The needle device disclosed in Japanese Laid-Open Utility Model NO. 30232/1985 involves a needle tube is formed with a longitudinally extending groove on the side wall thereof so as to allow the groove to serve as an air introducing passage.
Further, the needle device disclosed in Japanese Laid-Open Utility Model NO. 30233/1985 involves a needle tube contoured in a double walled structure so that the inner passage serves as a liquid delivering passage and the outer passage serves as an air introducing passage. Normally, the air introducing passage is fitted with a filter for preventing dust and bacteria in the air from being introduced into the interior of a container. Lately, the filter has been molded of hydrophobic material such as polytetrafluoroethylene resin or the like resin so to prevent liquid in the container from flowing back to the outside.
A needle device of the type including a liquid delivering passage and an air introducing passage extending in parallel with each other can be easily used, but it has several problems in that it is bulky and complicated in structure, resulting in increased production costs. With the needle devices which include an air introducing passage fitted with a filter made of hydrophobic material, if the liquid contains a surface active agent there arises the problem that the liquid is liable to gradually permeate through the filter. Another problem is that once the filter is filled with liquid, air permeates therethrough with much difficulty.